Getting rid of head lice permanently requires killing both live lice and their eggs, then preventing reinfestation over the following two to three weeks. Most people need at least two rounds of treatment spaced about a week apart, combined with thorough combing and basic household cleaning. The “permanently” part comes down to breaking the life cycle completely and stopping lice from coming back through reexposure.
Why Lice Keep Coming Back
Head lice have a three-stage life cycle that explains why a single treatment rarely works. Eggs (nits) hatch in 6 to 9 days. The newly hatched nymphs mature into egg-laying adults about 7 days later, and adults can survive on a human scalp for up to 30 days. If even a few eggs survive your first treatment, you’ll have a fresh generation of lice within two weeks. That’s why timing your second treatment to catch newly hatched nymphs before they can lay more eggs is the single most important step.
Over-the-Counter Treatments
The most common first-line option is permethrin lotion, available without a prescription at most pharmacies. It kills live lice by disrupting their nervous system, and studies show 50% to 97% of patients are lice-free at 14 days. The wide range in effectiveness reflects a growing problem: lice in many areas have developed resistance to permethrin and similar products. If you use permethrin and still see live lice crawling two or three days after treatment, resistance is likely the issue.
Dimethicone-based products work differently. Instead of poisoning lice, they physically coat and suffocate them by blocking their ability to manage water. Because the killing mechanism is physical rather than chemical, lice are far less likely to develop resistance. Clinical studies show dimethicone clears 70% to 96% of patients at 14 days. These products are widely available over the counter and are a good option if you suspect resistance to traditional treatments or prefer a non-pesticide approach.
Prescription Options for Stubborn Cases
When over-the-counter products fail, prescription treatments offer higher success rates. Spinosad is particularly effective because it kills both live lice and eggs in a single application, meaning you may not need a second round. In clinical trials, a single application of spinosad without any combing outperformed permethrin. It also has an extremely low toxicity profile, making it one of the safest prescription options available.
Other prescription choices include malathion lotion and oral ivermectin. Both are effective, but malathion tends to be expensive and ivermectin isn’t recommended for pregnant women. Your doctor can help you choose based on your situation, but if you’re dealing with lice that have survived one or two rounds of OTC treatment, asking about spinosad specifically is reasonable.
Wet Combing: The Non-Negotiable Step
No matter which product you use, combing is essential. Nit combs have teeth spaced closely enough to catch both live lice and the tiny eggs glued to individual hair strands. Flea combs designed for cats and dogs also work well.
The most effective technique is wet combing. Apply a generous amount of regular conditioner to damp hair, which slows lice down and makes them easier to catch. Work through small sections of hair from root to tip, wiping the comb on a white paper towel after each pass so you can see what you’re removing. After your initial treatment, comb and check the hair every 2 to 3 days for the next 2 to 3 weeks. This schedule lets you catch any nymphs that hatch from surviving eggs before they’re old enough to lay new ones.
Nits are cemented to the hair shaft with a protein-based glue that’s surprisingly tough. Enzyme-based nit removal products can help soften this glue, making combing faster and more thorough. Even without a special product, soaking hair in conditioner and combing methodically will remove the vast majority of eggs over several sessions.
Do Home Remedies Work?
Tea tree oil is the most studied natural remedy. A small trial of 26 schoolchildren using tea tree oil shampoo and conditioner showed a gradual reduction in infestation over four weeks, but the evidence is preliminary and far weaker than what exists for medical treatments. Tea tree oil might have some repellent or mild killing effect, but relying on it as your sole treatment is risky.
Mayonnaise, olive oil, and vinegar are popular suggestions online, but there’s no clinical evidence that any of them reliably kill lice or dissolve nit glue. The idea behind oil-based remedies is suffocation, but lice can close their breathing holes and survive for hours. If you want a suffocation-based approach, medical-grade dimethicone products are specifically designed for this and have clinical data behind them.
Cleaning Your Home the Right Way
Lice can only survive away from a human scalp for about one to two days, so household cleaning doesn’t need to be extreme. Focus on items that touched the infested person’s head in the two days before treatment:
- Bedding, towels, and clothing: Machine wash in hot water (at least 130°F) and dry on the highest heat setting.
- Combs and brushes: Soak in hot water (at least 130°F) for 5 to 10 minutes.
- Items you can’t wash: Seal in a plastic bag for two weeks. Any lice or nits inside will die without a host.
- Floors and furniture: A quick vacuum where the infested person sat or lay is enough. Skip fumigant sprays entirely. They’re unnecessary for lice and can be toxic.
Spending hours deep-cleaning your house won’t meaningfully reduce your risk. Lice spread almost exclusively through direct head-to-head contact, not from furniture or carpets.
Preventing Reinfestation
This is where “permanently” really matters. You can eliminate every louse and egg from your hair, then pick up a new case the following week from the same source. The most common cause of apparent treatment failure is actually reinfestation from a close contact who wasn’t treated.
Check everyone in the household. If one person has lice, it’s common for siblings or partners to have them too, and treating only one person while others remain infested guarantees the cycle continues. All infested household members should be treated on the same day.
Beyond your household, the CDC recommends these habits to reduce your risk going forward:
- Avoid head-to-head contact during play, sports, sleepovers, and similar activities. This is the primary way lice spread.
- Don’t share hair tools, hats, scarves, helmets, hair ties, or towels.
- Don’t share pillows or lie on bedding recently used by someone with lice.
The Complete Timeline
Here’s what a full elimination looks like from start to finish. On day one, apply your chosen treatment and do a thorough wet combing session. On days 3, 5, and 7, comb through the hair again to catch stragglers. Around day 7 to 9, apply a second treatment to kill any nymphs that hatched from surviving eggs (unless you used a product like spinosad that kills eggs too). Continue checking and combing every two to three days through day 21.
If you’re still finding live, crawling lice after two full rounds of the same product, switch to a different treatment class. Moving from permethrin to dimethicone, or from an OTC product to a prescription option, gives you the best chance of clearing a resistant infestation. By the three-week mark with no live lice found, you can be confident the infestation is gone.